1. Field of the Invention
This invention relates generally to centrifuge rotors, and relates more particularly to a rotor fabricated and reinforced with composite materials.
2. Description of the Relevant Art
Centrifuges are commonly used in medical and biological research for separating and purifying materials of differing densities, such as viruses, bacteria, cells, protein, and other compositions. A centrifuge includes a rotor typically capable of spinning at tens of thousands of revolutions per minute.
A preparative centrifuge rotor has some means for accepting tubes or bottles containing the samples to be centrifuged. Preparative rotors are commonly classified according to the orientation of the sample tubes or bottles. Vertical tube rotors carry the sample tubes or bottles in a vertical orientation, parallel to the vertical rotor axis. Fixed-angle rotors carry the sample tubes or bottles at an angle inclined with respect to the rotor axis, with the bottoms of the sample tubes being inclined away from the rotor axis so that centrifugal force during centrifugation forces the sample toward the bottom of the sample tube or bottle. Swinging bucket rotors have pivoting tube carriers that are upright when the rotor is stopped and that pivot the bottoms of the tubes outward under centrifugal force.
Many centrifuge rotors are fabricated from metal. Since weight is concern, titanium and aluminum are commonly used materials for metal centrifuge rotors.
Fiber-reinforced, composite structures have also been used for centrifuge rotors. Composite centrifuge rotors are typically made from laminated layers of carbon fibers embedded in an epoxy resin matrix. The fibers are arranged in multiple layers extending in varying directions at right angles to the rotor axis. During fabrication of such a rotor, the carbon fibers and resin matrix are cured under high pressure and temperature to produce a very strong but lightweight rotor. U.S. Pat. Nos. 4,781,669 and 4,790,808 are examples of this type of construction. Sometimes, fiber-reinforced composite rotors are wrapped circumferentially with an additional fiber-reinforced composite layer to increase the hoop strength of the rotor. See, for example, U.S. Pat. Nos. 3,913,828 and 4,468,269.
Composite centrifuge rotors are stronger and lighter than equivalent metal rotors, being perhaps 60% lighter than titanium and 40% lighter than aluminum rotors of equivalent size. The lighter weight of a composite rotor translates into a much smaller mass moment of inertia than that of a comparable metal rotor. The smaller moment of inertia of a composite rotor reduces acceleration and deceleration times of a centrifugation process, thereby resulting in quicker centrifugation runs. In addition, a composite rotor reduces the loads on the centrifugal drive unit as compared to an equivalent metal rotor, so that the motor driving the centrifuge will last longer. Composite rotors also have the advantage of lower kinetic energy than metal rotors due to the smaller mass moment of inertia for the same rotational speed, which reduces centrifuge damage in case of rotor failure. The materials used in composite rotors are resistant to corrosion against many solvents used in centrifugation. In a fixed-angle centrifuge rotor, several cell holes are machined or formed into the rotor at an angle of 5 to 45 degrees, typically, with respect to the rotor axis. The cell holes receive the sample tubes or bottles containing the samples to be centrifuged. Cell holes can be either through holes that extend through the bottom of the rotor, or blind holes that do not extend through the bottom. Through cell holes are easier to machine than blind cell holes, but require the use of sample tube holders inserted into the cell holes to receive and support the sample tubes.